Yellow Fever
|
Aedes aegypti. Image from CDC.
|
How is yellow fever transmitted?
There are two major transmission cycles for the yellow fever virus. In tropical rainforests, jungle yellow fever is mainly a disease of monkeys. Various species of Aedes or
Haemagogus mosquitoes transmit the virus from monkey-to-monkey. It is rare for humans to acquire this type of yellow fever but sporadic cases occur if people who visit or work in tropical rain forests are bitten by mosquitoes that have been infected by monkeys. Urban yellow fever, on the other hand, is a disease of humans. In towns, cities, or villages, the disease is spread by mosquitoes that have been infected by other people.
Aedes mosquitoes, primarily
Aedes aegypti, are the mosquitoes that transmit the yellow fever virus from human-to-human.
Aedes aegypti have adapted to living among humans. They breed in containers, such as discarded tires, flower pots, oil drums, and water storage barrels. Urban yellow fever is responsible for large-scale epidemics. A third type of yellow fever known as intermediate yellow fever is a rarer form of the disease and it only occurs in parts of Africa. Certain species of Aedes mosquitoes can infect both humans and monkeys, resulting in small-scale outbreaks over many separate villages in an area simultaneously. In all types of yellow fever cycles, mosquitoes pass the virus via their eggs (transovarial transmission) to the next generation of mosquitoes. The eggs are resistant to drying and lie dormant through dry conditions, hatching when the rainy season begins. Therefore, transmission is ensured from one year to the next.
| 
|
Yellow Fever Endemic Zone the Americas (CDC)
| Yellow Fever Endemic Zones Africa (CDC)
|
How common is yellow fever?
Over the past 400 years, yellow fever has caused epidemics involving thousands of deaths in North, Central, and South America, the Caribbean Islands, Africa and Europe. In the United States, significant outbreaks occurred in Philadelphia in 1793 (5,000 deaths) and Norfolk, Virginia in 1855 (3,000 deaths). Due in large part to development of a vaccine, as well as other preventive efforts such as intensive mosquito control programs, in the early 20th century, yellow fever is now limited to tropical parts of Africa (where the majority of cases occur), South America, and small areas of Central America and the Caribbean. However, many areas of the world are considered at risk because the appropriate mosquito vectors are present. The World Health Organization currently estimates that approximately 200,000 cases of yellow fever (with 30,000 deaths) occur every year in unvaccinated populations.
What are the symptoms of yellow fever?
Symptoms of yellow fever begin 3 to 6 days after being bitten by an infected mosquito. Although many yellow fever infections are mild or exhibit no symptoms whatsoever, the disease can cause severe, life-threatening illness. Symptoms include high fever, chills, headache, muscle aches, loss of appetite, nausea and/or vomiting. After 3 to 4 days, most patients improve and their symptoms disappear. However, in a small percentage of people (approximately 15%), after a brief recovery period of about 24 hours, severe symptoms rapidly develop, leading to shock, bleeding from the mouth, nose, eyes and stomach, and kidney and liver failure (with resulting jaundice). Half of the patients who develop severe symptoms die within 10 to 14 days, while the remainder recover without significant organ damage.
How is yellow fever diagnosed?
Yellow fever may be difficult to recognize, especially in the early stages. It may be easily confused with a wide variety of tropical diseases, including malaria, typhoid, rickettsial illnesses, hemorrhagic viral fevers (e.g. Lassa fever), arboviral infections (e.g. dengue), leptospirosis, and viral hepatitis. Yellow fever is confirmed by a blood test that detects yellow fever virus antibodies which are produced in response to the infection.
How is yellow fever treated?
There is no specific treatment for yellow fever. Appropriate supportive care is important. Dehydration and fever are common problems, so patients should rest and drink plenty of fluids. In severe cases, kidney dialysis may be necessary. Patients should be isolated from mosquitoes to prevent transmission to other people. Recovery from yellow fever is followed by lifelong immunity.
Is there a vaccine to prevent yellow fever?
. Yes. A very effective yellow fever vaccine is available. A single, subcutaneous injection confers immunity within 7-10 days in 99% of recipients. Protection lasts for at least 10 years, but likely 35 years or even much longer. Since there is no treatment for yellow fever, it is critical that persons planning to travel to endemic areas receive a vaccination.
Is there a way to reduce the risk of getting yellow fever?
The best way to prevent diseases spread by mosquitoes is to protect yourself from mosquito bites by using the DoD Insect Repellent System. It incorporates insect repellent on the uniform, DEET, picaridin, or IR3535 repellent on exposed skin, a properly worn uniform, and sleeping inside a insecticide-treated bed net.
Select the image for more information on the DoD Insect Repellent System.
